The 50-year-old has been in advanced talks with the club for the majority of the week, and succeeds Des Buckingham, who was sacked on Sunday.
It was revealed by this newspaper on Tuesday that United were looking for proven Sky Bet Championship experience and quality, and someone who can build and develop a squad in the long-term.
Rowett’s managerial CV would certainly suggest he fits those criteria.
READ ALSO: U’s skipper opens up on ‘shock’ Des Buckingham sacking
The former defender played for a host of Football League clubs and began his managerial career at Burton Albion in May 2012 following an initial caretaker stint.
He led the Brewers to two unsuccessful League Two play-off campaigns, and reportedly attracted the interest of the U’s in the post Chris Wilder era in 2014.
Rowett ultimately left the Brewers in October 2014 for Birmingham City in the Championship, and he spent just over two years at the club before being controversially sacked in December 2016 with the Blues seventh in the table.
He then joined fellow Championship side Derby County in March 2017, and guided the Rams to the 2018 play-off semi-finals, where they were beaten by Fulham.
Rowett switched to Stoke City soon after that play-off campaign, but was sacked in January 2019.
He was appointed Millwall boss in October 2019, and led the Lions to eighth place in the Championship, and then 11th, ninth and eighth in his three full seasons.
Rowett left the Lions by mutual consent in October last year, and returned to Birmingham in an interim role in March.
He was tasked with keeping the Blues in the Championship, but couldn’t maintain the club’s second tier status despite winning three and drawing two of their final eight matches.
United chairman Grant Ferguson told the club website: “Following a thorough and diligent recruitment process, I am delighted that Gary Rowett has agreed to join us as head coach.
“It was immediately clear from the discussions we had with him that Gary perfectly matched the vision and long-term objectives that we have for the club.
“Every decision taken is with the best interests of Oxford United in mind and we are confident that Gary will be instrumental in fulfilling our ambitions this season and beyond.
“We look forward to working alongside and supporting Gary to help us achieve our goals.”
U’s chief executive Tim Williams added: “To bring in a coach of Gary’s calibre and experience is a real statement of intent for this club.
“Gary is someone who will drive our standards every day at our training ground and help us in our ambition to become a competitive Championship club.
“His proven track record of delivering consistent success in the Championship makes him the ideal candidate to strengthen the team on the pitch, while we continue to make improvements off it.”
Rowett will be in the stands for United’s trip to Leeds United tomorrow.
He replaces Buckingham, who was dismissed after the side extended a dismal run of form to just one win in 15 games when they slipped to a 3-1 defeat at home against Sheffield Wednesday.
The loss left the U’s 20th in the Championship, a point clear of the relegation zone.
Oxford-born Buckingham’s sacking came as a shock to the United fanbase, with the club back in the second tier for the first time in 25 years.
It was Buckingham who guided the U’s to promotion via the League One play-offs last season, and thanks to an encouraging start which saw United win three of their first five league games this campaign, the side had yet to enter the bottom three.